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At least 109 records · Page 6Linked to original sources

Reading speed through different equivalent power low vision devices with identical field of view.

Adequate reading speed is one of the criteria low vision patients may use to assist them when they are comparing and selecting equivalent power low vision devices. Inherently, various optical devices of equivalent power will produce different fields of view. We compared the reading speed of 32 trained, normal observers with 4 commonly prescribed types of low vision devices of +12 D equivalent power (spectacles, hand magnifier, stand magnifier, and telemicroscope) which were modified to provide nearly identical fields of view. Our results show that only the reading speed obtained with the telemicroscope was significantly different from those of the other systems (p less than 0.01). Implications are that the field of view provided by a low vision device is the primary parameter limiting reading speed of equivalent power devices.

Adult↗

Prediction of simultaneously large and opposite generalized Goos-Hänchen shifts for TE and TM light beams in an asymmetric double-prism configuration.

It is predicted that large and opposite generalized Goos-Hänchen (GGH) shifts may occur simultaneously for TE and TM light beams upon reflection from an asymmetric double-prism configuration when the angle of incidence is below but near the critical angle for total reflection, which may lead to interesting applications in optical devices and integrated optics. Numerical simulations show that the magnitude of the GGH shift can be of the order of beam's width.

Journal Article↗

Large-scale synthesis of a novel tri(8-hydroxyquioline) aluminum nanostructure.

A novel tri(8-hydroxyquioline) aluminum (AlQ3) nanostructure was prepared on large scale at low cost by low-temperature physical vapor deposition (PVD). The morphologies, the chemical bondings, and photoluminescence of the AlQ3 nanostructure were investigated by environmental scanning electronic microscopy (ESEM), Fourier transform infrared spectrum (FT-IR), and photoluminescence (PL) spectra, respectively. The AlQ3 nanostructure was composed of micro-sphere with nanowire-cluster growing on the surface. The diameter of micro-sphere and nanowire were about 5 microm and 80 nm, respectively. FT-IR results indicated that the AlQ3 molecule had a strong thermal stability under research conditions. The growth mechanism of the novel nanostructure was discussed. The novel organic nanostructure would be believed to attractive building field-emission devices and other optical devices.

Aluminum↗

[Artificial cornea].

The cornea is the anterior transparent hole of the eye and its replacement by a synthetic material proves indispensable in some kinds of corneal blindness when penetrating keratoplasty is impossible. For a long time, the keratoprosthesis have been developed by different authors but results were always disappointing. Our personal works have been centered on the utilization of an expanded fluorocarbon polymer as interface between the optic of the keratoprosthesis and the cornea of the recipient. This material has given us a lot of satisfactions but our prosthesis did not meet the criteria of a real artificial cornea because the rigid optic induced mechanical tolerance problems and did not allow the measure of the intraocular pressure. We have developed a new model of artificial cornea with a soft optical zone with a diameter of 6 mm and an haptic made of expanded fluorocarbon polymer pretreated in order to induce a fast cellular ingrowth. We hope that this new optical device could improve optical results and tolerance.

Cornea↗

A video-based optical system for rapid measurements of chest wall movement.

We tested apparatus developed to measure the movement of the surface of the chest and abdomen, during breathing in the supine subject. A line of light is projected onto the chest wall. The line image from a video camera is analysed to estimate of the height of the surface profile, so that the shape and volume of the object can be derived. The data can provide direct or inferential volume estimates. We compared this system with the widely used inferential system of inductance bands in supine volunteers who breathed using patterns designed to emphasize variability in movements: normal and large breaths, and breathing through an expiratory resistance. We calculated the differences between a spirometer signal and continuous volume estimates using the linear regression method, obtained using signals from the two methods. The volume estimate differences obtained by the optical system and induction bands were not significantly different, but the optical system was more precise. Using the optical device, an acceptable interquartile range of differences from spirometric volume (50 ml) was significantly likely when the optical device was used. During resistive loaded breathing (mean tidal volume 390 ml) direct optical measurements of volume, and inductance band estimates, were compared with tidal volume. The optical system showed distortion of the shape of the abdomen during this breathing pattern. Mean error with the optical system was 64 ml and with the inductance band system was 108 ml (p < 0.05). The optical system gives accurate reproducible results in supine human subjects and additional valuable information on shape changes.

Abdomen↗

Characteristics of a charged-coupled-device-based optical mapping system for the study of cardiac arrhythmias.

We develop an optical fluorescent mapping system that is able to record the action potential wavefront propagation within cardiac tissue samples with high spatial and temporal resolutions. The system's main component, the fluorescence acquisition device (customized CCD camera), offers a high spatial resolution of 128 x 128 pixels, with 12-bit digitization and a frame rate of 490 frames/s. The system is designed and implemented to image an area of approximately 20 x 20 mm at its minimum object distance of 140 mm, corresponding to a spatial resolution of approximately 3 line pairs/mm. Experiments using this system with di-4-ANEPPS-stained canine cardiac tissues with stimulated action potentials through external electrodes result in successful mappings of the distribution and propagation of the action potential wavefronts, showing the system's sensitivity to the change in fluorescence intensity in regions of action potentials. These data demonstrate this optical mapping system as a powerful device in the study of cardiac arrhythmia mechanisms.

Action Potentials↗

Long-lived transient behavior in an n+-n-n+ semiconductor device with optical stochasticity.

We numerically study the response time of an ultrafast microwave switch, i.e., a GaAs-based Gunn device, under stochastic stimuli. The conducting states in this semiconductor device can be controlled in the presence of laser illumination near the doping notch. With the consideration of the additional randomness in laser intensity, the switching time from the initial unstable state to the final stable state will increase. Therefore, the so-called noise delayed decay of unstable states in an n+-n-n+ semiconductor device is demonstrated.

Journal Article↗

[System continuity and energy distribution in laser-induced thermo therapy (LITT)].

PURPOSE: Evaluation of the continuity and energy distribution of a laser system for laser-induced thermo therapy. MATERIAL AND METHODS: For evaluation of the continuity of laser optical devices, laser generating units and optical fibers of three different manufactures (Dornier, Hüttinger, Somatex), we used the equipment to generate a laser beam of 25 Watt for 60 minutes. Measurements of the applied energy were done sequentially with two MY Test (Fa. Hüttinger) units. We also performed two in vitro ablations of animal liver tissue with different fiber optics [Mikrodom A 13-0540, Microflexx REF A 13-0561 (Hüttinger), Diffusor-Tip H-6111-T 3, Diffusor H-6111-T 4 (Dornier), Somaflex-Diffusor (Somatex)] over 20 minutes at- an energy flow of 25 J per second. We then evaluated the geometry of coagulation. RESULTS: The different equipment used for our tests showed differences of a maximum of 10 %. Some components did not work properly in certain configurations even though the manufacturer assured it would. We saw significant differences in the ablation characteristics of the different fiber optics, especially in axial and frontal directions. CONCLUSION: Knowledge of the different characteristics in energy distribution and ablation characteristics are an important factor in performing a successful laser-induced thermo therapy.

Animals↗

Principles of modern low vision rehabilitation.

Low vision rehabilitation is a new emerging subspecialty drawing from the traditional fields of ophthalmology, optometry, occupational therapy, and sociology, with an ever-increasing impact on our customary concepts of research, education, and services for the visually impaired patient. A multidisciplinary approach and coordinated effort are necessary to take advantage of new scientific advances and achieve optimal results for the patient. Accordingly, the intent of this paper is to outline the principles and details of a modern low vision rehabilitation service. All rehabilitation attempts must start with a first hand interview (the intake) for assessing functionality and priority tasks for rehabilitation, as well as assessing the patient's all-important cognitive skills. The assessment of residual visual functions follows the intake and offers a unique opportunity to measure, evaluate, and document accurately the extent of functional loss sustained by the patient from disease. An accurate assessment of residual visual functions includes assessment of visual acuity, contrast sensitivity, binocularity, refractive errors, perimetry, oculomotor functions, cortical visual integration, and light characteristics affecting visual functions. Functional vision assessment in low vision rehabilitation measures how well one uses residual visual functions to perform routine tasks, using different items under various conditions, throughout the day. Of the many functional vision skills known, reading skills is an obligatory item for all low vision rehabilitation assessments. Results of assessment guide rehabilitation professionals in developing rehabilitation plans for the individual and recommending appropriate low vision devices. The outcome from assessing residual visual functions is detection of visual functions that can be improved with the use of optical devices. Methods for prescribing devices such as image relocation with prisms to a preferred retinal locus, field displacement to primary gaze position, field expansion, and manipulation of light are practiced today in addition to, or instead of, magnification. Correction of refractive errors, occlusion therapy, enhancement of oculomotor skills, and field restitution are additional methods now available for prescribing devices leading to rehabilitation of visual functions. The outcome from assessing residual functional vision is detection of functional vision that can be improved with the use of vision therapy training. After restoration of optimal residual visual functions is achieved with optical devices, one can follow with training programs for restoration of lost vision-related skills. If an optical dispensary is available where prescribing of low vision devices routinely take place, this will help ensure familiarity and specialization of the dispensary and staff with low vision devices and their special dispensing requirements. The dispensing of low vision devices is an opportunity to introduce the device to the patient, train the patient in the correct use of the device for the task selected, and create a direct and continuous connection with the patient until the next encounter. Following assessment, prescribing, and dispensing of devices, a low vision practitioner, ophthalmologist or optometrist, is responsible for recommending and prescribing vision therapy training to improve residual functional vision. An attempt to present a template for a comprehensive modern low vision rehabilitation practice is made here by summarizing scientific developments in the field and stressing the multidisciplinary involvement required for this kind of practice. It is hoped that this paper and other initiatives from colleagues, the public, and government will promote and raise awareness of modern low vision rehabilitation for the benefit of all.

Humans↗

Molecular optical gating devices based on polymer nanosheets assemblies.

We describe here a polymer nanosheet assembly that serves as a molecular photoswitching and optical exclusive OR (EXOR) logic gate. Separate polymer nanosheets (monolayers) containing phenanthrene, anthracene, and dinitrobenzene chromophore were prepared by the Langmuir-Blodgett technique (LB films). A bilayer-couple, consisting of phenanthrene (sensitizer) monolayer and dinitrobenzene (acceptor) monolayer, and the other couple, of anthracene monolayer and dinitrobenzene monolayer, were confirmed to function as a photodiode showing current rectification on light irradiation. The two photodiodes are connected as each photocurrent direction becomes opposite. In the polymer photodiode array (LB films), anodic photocurrent was observed when the anthracene was selectively excited. On the other hand, cathodic photocurrent was observed by selective excitation of the phenanthrene. Moreover, the output photocurrent displayed a very small value when the phenanthrene and anthracene were excited simultaneously. The performance is discussed for this gate's application to an optical EXOR logic gate.

Journal Article↗

A three-dimensional optical photonic crystal with designed point defects.

Photonic crystals offer unprecedented opportunities for miniaturization and integration of optical devices. They also exhibit a variety of new physical phenomena, including suppression or enhancement of spontaneous emission, low-threshold lasing, and quantum information processing. Various techniques for the fabrication of three-dimensional (3D) photonic crystals--such as silicon micromachining, wafer fusion bonding, holographic lithography, self-assembly, angled-etching, micromanipulation, glancing-angle deposition and auto-cloning--have been proposed and demonstrated with different levels of success. However, a critical step towards the fabrication of functional 3D devices, that is, the incorporation of microcavities or waveguides in a controllable way, has not been achieved at optical wavelengths. Here we present the fabrication of 3D photonic crystals that are particularly suited for optical device integration using a lithographic layer-by-layer approach. Point-defect microcavities are introduced during the fabrication process and optical measurements show they have resonant signatures around telecommunications wavelengths (1.3-1.5 microm). Measurements of reflectance and transmittance at near-infrared are in good agreement with numerical simulations.

Journal Article↗

Time-resolved spectroscopy of organic dendrimers and branched chromophores.

Organic dendrimers have been considered for a number of optical applications and are now of great interest for the purpose of enhanced nonlinear optical effects. In order to understand the mechanism of the enhanced effects in branched structures it is important to probe the fundamental excitations and the degree of intramolecular interactions utilizing various spectroscopic techniques. In this review, the nonlinear optical and excited state dynamics of different dendritic and other branching chromophore structures are discussed. The methods of two-photon absorption, time-resolved fluorescence, transient absorption, and three-pulse photon echo peak shift are discussed in regards to the degree of intramolecular coupling in the macromolecular systems. These techniques are also used for a comparison of the dynamics in the linear molecular analog systems as well. Thus, this review focuses on the aspect of intramolecular interactions in a branched system and its importance to enhanced nonlinear optical effects useful for modern optical devices.

Absorption↗

Optical integrating balloon device for photodynamic therapy.

BACKGROUND AND OBJECTIVES: It is difficult to deliver light uniformly and efficiently over the complex shapes presented by various organs for photodynamic therapy (PDT). A balloon delivery device for photodynamic therapy was designed and tested for treatment of various anatomic tissues. The device uses the principle of optical integration by multiple internal diffuse reflections to achieve uniform output illumination. STUDY DESIGN/MATERIALS AND METHODS: Soft, white, medical-grade silicone balloons were made in various shapes and tested for optical output, uniformity, efficiency, and power capabilities. Balloons were cast to be approximately the shape of the target tissue surface, organ, or cavity. Laser power was introduced into the saline-filled balloon by one or more fiber optics. Devices were constructed and used to illuminate oral mucosa and uterine endometrium for PDT. RESULTS: The balloon walls had low optical absorption, high diffuse reflectivity (80-95%), and low diffuse transmittance (5-20%) in the 500- to 900-nm wavelength region. Optical efficiencies of 65% were typical with emitted light over complex, nonspherical surfaces. Efficiency increased with inflation of the device, such that irradiance (power/area) at the balloon surface was nearly constant with inflation. CONCLUSION: Optically integrating balloons can provide highly uniform, efficient light exposure over complex tissue surfaces. Uniformity and irradiance were not strongly affected by balloon inflation, and these robust devices are easy to produce in essentially any shape.

Catheterization↗

Beam expansion in thermo-optic-effect-induced total internal reflection and its applications in optical switches.

The beam-propagation characteristics of the total internal reflection (TIR) induced by the thermo-optic effect are investigated. Based on the Fourier heat-transmission principle and the variable separation method, we derive an analytical transient expression of the thermal field for general thermo-optic devices. With the analytical expression, the time response and steady-state temperature distribution of thermo-optic devices are presented. The beam expansion rule of TIR in the thermal field is developed mathematically, and a quantitative calculation is given as well. To illustrate the application of the rule, an X-junction 2 x 2 TIR switch with high reflection efficiency is designed through theoretical calculation. The simulation shows that the structure exhibits a high reflection coefficient; the reflection loss is only -0.76 dB. The simulation results agree well with the theoretical calculation.

Journal Article↗

Current Treatment of Nystagmus.

Acquired and congenital nystagmus often causes decreased visual acuity as a direct result of the inability to maintain stable foveal vision. In addition, acquired nystagmus causes a disabling subjective sensation of movement of the visual world called oscillopsia. The eye movements themselves do not require treatment if the patient is asymptomatic. However, therapy is necessary if visual disability is present. Treatments based in pharmacologic mechanisms are preferred. There are few controlled treatment trials and therapeutic efficacy generally is sought in a trial and error approach, depending on the type of nystagmus present. Treatment with 3,4-diaminopyridine and 4-aminopyridine recently have been shown to be effective for downbeat nystagmus. Gabapentin, baclofen, and clonazepam also are useful in some patients with downbeat nystagmus. Baclofen is the therapy of choice for periodic alternating nystagmus. Gabapentin often is effective for acquired pendular nystagmus. Clonazepam and valproate also may be effective for acquired pendular nystagmus. Memantine now is available in the United States and is promising in the treatment of pendular nystagmus. Optical devices that negate the negative effects of nystagmus continue to undergo development research. These and other medical, surgical, and optical devices are potentially useful alone or in combination with other therapies.

Journal Article↗

Quantum optical coherence in cytoskeletal microtubules: implications for brain function.

'Laser-like,' long-range coherent quantum phenomena may occur biologically within cytoskeletal microtubules. This paper presents a theoretical prediction of the occurrence in biological media of the phenomena which we term 'superradiance' and 'self-induced transparency'. Interactions between the electric dipole field of water molecules confined within the hollow core of microtubules and the quantized electromagnetic radiation field are considered, and microtubules are theorized to play the roles of non-linear coherent optical devices. Superradiance is a specific quantum mechanical ordering phenomenon with characteristic times much shorter than those of thermal interaction. Consequently, optical signalling (and computation) in microtubules would be free from both thermal noise and loss. Superradiant optical computing in networks of microtubules and other cytoskeletal structures may provide a basis for biomolecular cognition and a substrate for consciousness.

Animals↗

Vision readiness at Seymour Johnson Air Force Base.

Ensuring that our forces are vision ready, i.e., they have the appropriate visual acuity, optical devices, and eye health to perform their mission, is essential on today's battlefield. A study was conducted at Seymour Johnson Air Force Base to determine the prevalence of vision readiness in a deploying fighter squadron. Of the 204 personnel screened, 59 wore glasses or contact lenses. Of these 59, 15 individuals (25%) were optically ready and 44 individuals (75%) were not optically ready to deploy. Optical readiness is defined as having the correct type and number of optical devices. Of the 15 individuals (25%) who were optically ready, 13 (87%) had had a professional eye examination within 12 months. Of the 44 individuals (75%) who were not optically ready, 36 (82%) had been examined within 1 year. Pearson's chi 2 test (chi 2 = 1.59, degrees of freedom = 3, significance = 0.66) indicated that there was no significant association between readiness and the date of the last examination. This study reveals that although personnel are having regular periodic professional eye examinations, optometry personnel, commanders, and deploying airmen must take a more active role in ensuring that our forces are vision ready.

Aerospace Medicine↗